What's the difference between Continuous RMS and Dynamic Power ?

Last Update: 06/16/2012

Many people confuse these specifications, so I will try to give you a simplified, non-technical explanation. Continuous RMS Power, is the spec that really tells you how powerful an amplifier is. RMS power is expressed in watts. A typical specification might read 100 watts RMS into 8 ohms from 20Hz-20KHz at .01% THD. What this means, basically, is that the amplifier will deliver 100 watts into an 8-ohm speaker from 20Hz to 20Khz? This frequency range is basically the entire audio range that an individual can hear. The THD spec stands for Total Harmonic Distortion: This is the amount of distortion the amplifier will introduce into the original signal. Any high quality amp made today has extremely low distortion ratings. The human ear cannot hear anything under 2%. For the most part, when you are considering purchasing an amplifier, you can disregard the THD specifications. Dynamic Power, is a little more difficult to understand. This is a test of the amplifier's ability to go beyond its continuous RMS power for a very short time period. We are not talking minutes or even seconds here. We are talking milliseconds or thousandths of a second. A musical transient peak, such as a cymbal crash lasts only a very short time. Dynamic power is usually measured into 8 ohms, but specifications are generally also published for 2, 4, and 6 ohm loads as well. To keep things from getting too complicated, we will concentrate on the 8-ohm figures. To measure dynamic power, an amplifier is fed a 1000 Hz signal for 20 milliseconds then allowed to rest for 480 milliseconds. The amplifier volume control is turned up until the amp reaches the clipping point. At that point, the amp has reached its instantaneous peak or dynamic power output. Like the continuous power rating, dynamic power is expressed in watts. The figure is usually significantly larger than the RMS power rating, and should not be confused with the continuous power ratings of the amplifier. A dynamic power rating into a figure such as 1 or 2 ohms does not mean that the amplifier can drive a speaker with a 1 or 2 ohm rating continuously. If you attempt that, the amplifier will either go into the protection mode or possibly cause damage.

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